A method is known (EU-PA No. 00 20 456) for the production of transparent heat mirrors by depositing a film of mixed indium oxide or mixed tin oxide on a substrate, in which a low-temperature deposition on a polymer substrate by sputtering, thermal evaporation, vacuum depositing or electron bombardment is employed, and an oxygen partial pressure is used during the deposit which directly produces films of the above-named material with a high transparency and a high reflectivity.
In the apparatus used for the practice of this method, a water-cooled target is disposed at an angle of about 45.degree. with respect to the ion beam produced by a radiation source in the vacuum chamber provided with a gas inlet, the ejected target source material producing a coating on the substrate which is at an angle to the target and coated with a polymer.
A plasma generator with an ion beam producer is disclosed by Goebel, Campbell, and Conn, Journal of Nuclear Materials, 121:277-282 (1984), North Holland Physics Publishing Division, Amsterdam; Hirooka et al., Journal of Nuclear Materials, 141-143:193-197 (1986) North-Holland Phys. Publishing Div., Amsterdam; and Goebel et. al, Journal of Nuclear Materials, 145-147:61-70 (1987) North-Holland, Amsterdam.
The Goebel et al plasma generator is disposed in a separate chamber connected to the vacuum chamber, while the approximately cylindrical wall of the separate chamber forms the anode and is provided with an inlet connection for the process gas. An accelerator is situated on a part of the wall that closes the one end of the cylindrical chamber and faces away from the actual vacuum chamber Bias is supplied to the sample or target in the generator to induce sample erosion in order to study the effects of the plasma on different materials.
The Goebel et al generator produces a small cylindrical plasma, and cannot achieve high sputtering rates because the voltage that can be applied to the target is limited. The maximum voltage that can be applied to the target surface is only 300 volts and current densities of only up to 1 amp per square centimeter were achieved.
The present invention provides apparatus for high-rate sputtering and/or evaporation of metallic or dielectric materials by means of an externally produced plasma of large area and varied cross-sectional shape. The power applied to the target is significantly greater than in prior art devices such as magnetrons and diodes. The construction of the apparatus is simple and the plasma is produced independently of the target. Target voltage and the target current can be adjusted independently of one another, in this apparatus in contrast to prior art systems.
In contrast to this, prior art magnetron devices required operating pressures in the 3-10 millitorr range and, at these pressures, the mean-free path of a sputtered atom is only a centimeter at best. Because of this short path length, sputtered material is scattered before it reaches the substrate. Typically, energies of 400-600 eV are needed to achieve useful magnetron sputtering rates, but at these energy levels substrates and targets are significantly damaged and various chemical reactions at the target surface are inhibited. See U.S. Pat. No. 4,588,490 owned by IBM. Magnetron systems are also material specific which means that the yield of secondary electrons from a target surface determines the properties of the plasma. Furthermore, the effect of magnetic drift (ExB) on sputtering wherein electrical lines of force (E) cross magnetic lines of force (B) is a well known phenomenon, as explained by Penning (U.S. Pat. No. 2,146,025) and Chapin (U.S. Pat. No. 4,166,018) .
In the present invention it is possible to convert coating systems using conventional, magnetic field-supported cathode sputtering to cathode sputtering with an externally produced plasma. Also, the useful target thickness is as great as possible and its ablation is as uniform as possible.